A LIGHT REFLECTANCE TECHNIQUE FOR THICKNESS MEASUREMENTS OF PASSIVE FILMS

A new in situ technique to determine the thickness of passive films is reported. In the present work, this technique is applied to the passi ve film on iron in berate buffer. The method is based on the light abs orption of the oxide film for light energies higher than the band gap energy of the oxide. By using laser lines of 325 nm and 441 nm, the li ght absorption in the passive film on iron becomes accessible by measu ring the difference in the reflectance of the electrode surface prior to and after passivation. The results for the absorption coefficient a nd for the film thickness obtained with this technique are in good agr eement with values from the literature. (C) 1997 Elsevier Science Ltd.